Run-Run join is not allowed of they have same "Start With Riser"/"End With Riser" configuration at the joined end.
Namespace: Autodesk.Revit.DB
Assembly: RevitAPI (in RevitAPI.dll) Version: 26.2.0.0 (26.2.0.0)
Syntax
C#
public static FailureDefinitionId StairsRunRunJoinNotAllowedFailure { get; }